It is desired to control muzzle velocity of projectiles discharged from a firearm for various purposes. Two examples of the desire to control muzzle velocity would be to control the penetration of the projectile into a target, and, secondly, to control the environmental impact of the discharge of the weapon, particularly in abatement of noise. The prior art solution in controlling the muzzle velocity of the projectile discharged from the firearm was to adjust the amount of powder contained in the cartridge which was detonated in the firearm, and thus control the amount of force developed to propel the projectile from the barrel of the firearm. This meant that the operator of the firearm had to select a cartridge with a particular amount of powder therein, depending upon the muzzle velocity the operator desired upon discharge of the projectile from the firearm. It has long been desired to have a means of control of the muzzle velocity of the projectile discharged from a firearm wherein a cartridge with a standard amount of powder could be used and the control of the muzzle velocity would reside in something other than the amount of powder in the cartridge. The present invention achieves this effect by providing for a modification of the barrel of the firearm in such a manner so as to produce a unique control of the muzzle velocity of a projectile.